1. Field of the Invention
The invention relates to the steering control of rocket propelled vehicles by the use of thrust direction control or a combination of thrust direction control and steering fin control.
2. Description of the Related Art
As military aircraft become faster and more maneuverable, there is an increased need for faster and more maneuverable missiles with longer ranges to counter these threats. One method of increasing maneuverability of a missile is to use a steerable nozzle on the rocket motor to allow the direction of thrust to be controlled. This affords greater maneuverability than traditional movable aerodynamic fins alone can provide under low speed or very high altitude when the dynamic pressure is low.
The mechanism used to move the steerable nozzle is known as the nozzle actuator system. Such a system is disclosed in U.S. Pat. No. 5,505,408 of John M. Speicher, Allan A. Voigt and Che-Ram S. Voigt, assigned to the same assignee as the instant application. The disclosure of that patent is incorporated herein by reference. That system has a pair of orthogonal yoke plates used to direct a rocket nozzle in accordance with steering commands of the missile control system. The yoke plates are coupled to the rocket nozzle, which is pivoted for movement at a ball-and-socket type joint, such that their translation in their prescribed planes moves the rocket nozzle to effect directional control of the rocket thrust.
A shortcoming of the prior art is that, although thrust direction control may provide adequate control of the missile along the yaw and pitch axes, motion along the roll axis must still be effected through the use of the missile aerofins. A problem arises at high altitudes, however, under conditions of low dynamic pressure, such as high angles of attack and low speeds, which significantly reduce the effectiveness of the aerofins. This reduces roll motion control and compromises the stability and maneuverability of the rocket.
Attempts to obviate problems with reliance on aerofins for roll motion control have included the use of a plurality of rocket nozzles. Such a system is disclosed in U.S. Pat. No. 3,200,586. The need to independently control the rocket nozzles in such a system, however, detracts from its practicability by adding additional weight and expense and reducing the reliability of the rocket.
Other systems, such as those disclosed in U.S. Pat. Nos. 3,786,993 and 3,986,683, have used a single nozzle in conjunction with movable tabs disposed in the exhaust stream. However, in addition to increasing costs, these systems also introduce drag, which results in a host of attendant complications.
U.S. Pat. No. 3,200,587 discloses still another system which provides attitude control of a rocket vehicle by shifting the nozzle transversely so that the thrust axis is no longer coincident with the central axis of the vehicle, thereby developing steering torque.